The present application is based on and claims priority from Japanese Patent Application 2000-97905 filed Mar. 30, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to various indicating instruments including a vehicular indicating instrument.
2. Description of the Related Art
In a vehicular indicating instrument, a drive unit has a drive control section disposed behind a dial plate and a rotary shaft extending through the dial plate to carry a pointer at the end thereof. The rotary shaft is connected to an output gear of a speed reduction gear train. The rotary shaft is usually made of a metal shaft that is integrated with the output gear.
Because the rotary shaft is considerably long and thin in order to provide a smooth and accurate operation of the pointer, it is very difficult to provide a sufficient bending strength. Therefore, the rotary shaft has to be very carefully handled not to bend when it is machined or heat-treated.
A main object of the invention is to provide an indicating instrument that has an improved rotary shaft.
Another object of the invention is to provide a rotary shaft that has a sufficient bending strength without sacrificing smooth and accurate operation of the pointer.
An indicating instrument according to a preferred embodiment of the invention includes a dial plate, a drive unit having a casing disposed behind the dial plate, a drive control section disposed in the casing, a rotary shaft driven by the drive control section and a pair of bearings fixed to the casing and a pointer carried by the rotary shaft. According to a feature of the invention, the rotary shaft is comprised of a thin shaft supported by at least one of the bearings disposed near the dial plate and a thick shaft having an end connected to the thin shaft, and the thin shaft has such a length and an outside diameter that the ratio of said length to said outside diameter provides a sufficient bending strength.
The rotary shaft may further include another thin shaft supported by the other of the pair of bearings, and the thick shaft has the other end connected to the other thin shaft, and the other thin shaft has also such a length and an outside diameter that the ratio of said length to said outside diameter provides a sufficient bending strength.
The thin shaft may be a stainless steel member, and the thick shaft may be a resinous member. The drive control section may include a speed reduction gear train having an output gear. In such a case the thick shaft may be integrated with the output gear. The ratio of each thin shaft, is, preferably, less than 10. The length of each thin shaft may be less than 10 mm, and the outside diameter of each thin shaft may be about 1 mm. Further, the thick shaft may be made of one of materials consisting of polyacetal and polyphenylene sulfide.